Heat sink for a semiconductor chip device

ABSTRACT

A heat sink for a semiconductor chip device includes cavities in a lower surface thereof for receiving electrical components on a top surface of the semiconductor chip, and a pedestal extending through an opening in the semiconductor chip for contacting electrical components on a bottom surface of the semiconductor chip. A lid may also be provided on the bottom surface of the semiconductor chip for protecting the electrical components and for heat sinking the electrical components to an adjacent device or printed circuit board.

TECHNICAL FIELD

The present invention relates to a heat sink for a semiconductor chipdevice, and in particular to a heat sink for a dual-sided semiconductorchip device.

BACKGROUND

As electrical power dissipation increases in electronic integratedcircuits (IC) or photonic integrated circuit (PIC), keeping theoperational temperatures of every component of a semiconductor chipdevice within an acceptable range using traditional electronic packagingmethods becomes increasingly more difficult.

IC devices are typically bonded to a substrate of some kind, whichincludes electrical traces extending out to the edge of the package withadditional electronic components connected along the way. If the powerdissipation of the device is high, the substrate may be bonded to a heatsink for dissipating heat. However, the interface between the substrateand the heat sink can prove to be a significant thermal barrier, therebyincreasing operational temperatures beyond what is required by thedevice to operate efficiently. Furthermore, it is usually only possibleto direct the excess heat from the device along one interface, e.g.toward the heat sink. With a mixture of components, which are bonded ina variety of different ways, e.g. ball grid array (BGA) and directbonding methods, optimally dissipating heat from all the components onthe substrate becomes increasingly more difficult.

An object of the present invention is to overcome the shortcomings ofthe prior art by providing a heat sink for a dual-sided semiconductorchip device.

SUMMARY OF THE INVENTION

In accordance with one embodiment, a semiconductor chip device comprisesa substrate including first and second sides, and an opening extendingthrough the substrate between the first and second sides; firstopto-electronic or electronic components mounted on the first and secondsides; a heat sink mounted on the first surface in thermal contact withthe components on the first side, and including an extension extendingthrough the opening with an exposed surface parallel with the secondside; and at least one second opto-electronic or electronic componentsmounted on the exposed surface of the extension; wherein the heat sinkprovides a first thermally-conductive path for the first components onthe first side and each of the second components on the exposed surface.

In accordance with a modified embodiment, a heat sink comprises a basefor mounting on a first side of a substrate; thermally conductive pinsor fins extending from a first side of the base away from the substrateproviding a first thermally conductive path; cavities extending into asecond side of the base for receiving opto-electronic or electroniccomponents mounted on the first side of the substrate for physically andRF shielding the opto-electronic or electronic components; and anextension extending from the second side of the base to extend throughan opening in the substrate to a second side of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described in greater detail with reference to theaccompanying drawings which represent preferred embodiments thereof,wherein:

FIG. 1 is a diagram of an isometric view of a semiconductor chip deviceof the present invention;

FIG. 2 is a diagram of a side view of the semiconductor chip device ofFIG. 1; and

FIG. 3 is diagram of an isometric view of the semiconductor chip deviceof FIG. 1 including a bottom lid.

DETAILED DESCRIPTION

While the present teachings are described in conjunction with variousembodiments and examples, it is not intended that the present teachingsbe limited to such embodiments. On the contrary, the present teachingsencompass various alternatives and equivalents, as will be appreciatedby those of skill in the art.

With reference to FIGS. 1 and 2, an electronic (IC) or opto-electronic(PIC) chip device 1 includes a substrate 2, comprising, for example, asemiconductor printed circuit board (PCB) or a more thermally conductivematerial, such as aluminum nitride. Active opto-electronic and/orelectronic components 3 are mounted on first and second surfaces orsides 4 and 5, respectively, of the substrate 2. In the illustratedembodiment the first and second surfaces or sides 4 and 5 are oppositeupper and lower surfaces or sides of the substrate 2. A heat sink 11 ismounted on one of the first and second surfaces or sides 4 and 5,respectively, and includes a base 10 with one or more cavities 12extending into the base 10 from a bottom surface thereof, and heatdissipated pins or fins 13 extending outwardly, e.g. upwardly, from anupper side thereof to facilitate heat dissipation away from thesubstrate 2. The depth of each of the cavities 12 may be substantiallythe same as the height of a corresponding one of the components 3received therein, so that the corresponding components 3 may be bondeddirectly to the bottom surface of the cavities 12 in the heat sink 11for conducting heat, while the base 10 of the heat sink 11 may still becoupled to the substrate 2, at least partially around the peripherythereof, e.g. along side walls of the base 10.

Ideally, the heat sink 11 is comprised of a thermally and electricallyconductive material, e.g., a metal, such as an aluminum alloy (167 W/m°K) or copper (350 W/m° K), which has a thermal conductivity greater than150 W/m° K. Since the heat sink 11 conducts electricity, the heat sink11 may become an electrical ground for the components 3, and may alsoprovide RF shielding, if the components 3 and the heat sink 11 arebonded using an electrical conductive material, such as solder orconductive epoxy such as a silver-filled epoxy.

The substrate 2 includes at least one opening 14 extending therethroughfrom the first surface 4 to the second surface 5 for receiving a heatsink extension, e.g. a pedestal portion 15, extending from a bottomsurface of the base 10 of the heat sink 11 below the plane of the bottomsurface of the base 10. The pedestal portion 15 may be fixed to thesubstrate 2 using an epoxy or solder at the edge of the opening 14 andthe periphery of the pedestal portion 15. The pedestal portion 15 mayextend through the opening 14, whereby an exposed surface of thepedestal portion 15 is parallel to or ideally coplanar with the secondsurface 5 of the substrate 2.

One or more high power IC or PIC 33 may be mounted directly on theexposed surface of the pedestal portion 15. The high power PICs maycomprise a laser for generating an optical signal for transmission on afirst optical fiber 34 optically coupled to one of the high power PICs33, e.g. to an edge of the substrate 2. The high power PICs 33 may alsoinclude a photodetector for receiving light from a second optical fiber35 optically coupled to the photodetector, e.g. to an edge of thesubstrate 2, thereby forming a bidirectional transceiver. The high powerPIC's may also include trans-impedance amplifier (TIA) chips 36 and RFlaser drivers 37.

The heat sink 11 may be manufactured in an extrusion process, therebymaking the cross section, i.e. the cavities 12, the side walls of thebase 10, and the pedestal portion 15, the same relative heights andwidths along the length of the heat sink 11, and the ends of the heatsink 11 open. However, the open ends of the heat sink 11 may be closedoff by soldering a block to the substrate 2, e.g. soldered at the sametime as the components 3, which would prevent warping of the substrate 2when under clamping pressure. Moreover, a closed off cavity 12 mayimprove physical and RF shielding of the components 3, if necessary.However, having air flow through the cavities 12, when the ends areopen, may be beneficial in terms of heat removal, for some applications.

Optionally, instead of the pedestal portion 15 being a single monolithicstructure, i.e. integral with the remainder of the heat sink 11, theheat sink 11 may include one or more separate heat spreaders 16 attachedto the bottom surface of the base 12 of the heat sink 11 to extendthrough the at least one opening 14 for supporting the high power IC′ orPIC's 33 on a exposed surface of the heat spreader 16 to at leastpartially compensate for possible thermal expansion or bonding issuesbetween the heat sink 11 and the high power IC's 33. The optional heatspreader 16 may be comprised of a material with high thermalconductivity, e.g. greater than 150 W/mK, preferably greater than 175W/m° K, but with a lower coefficient of thermal expansion (CTE), e.g.less than 20×10⁻⁶ m/(m° K) @ 25° C., preferably less than 10×10⁻⁶ m/(m°K) @ 25° C. than the heat sink 11. Examples of suitable materials arecopper (I>400 W/m° K, a<16.8×10⁻⁶ m/(m° K @25° C.), CVD diamond (I>1800W/m° K, a<1.0×10⁻⁶/K @25° C.), AlSiC (I>170 W/m° K, a<10.9×10⁻⁶ m/(m° K)@25° C.), Aluminum-Nitride (I>170 W/m° K, a<4.2×10⁻⁶ m/(m° K) @° 25°C.), Copper-Tungsten (I>170 W/m° K, a<8.3×10⁻⁶ (m/m° K) @ 25° C.) orother high thermal conductivity and low thermal expansion material.

Electrical connection may be made between the high power IC's 33 and tothe substrate 2 by using wire-bonds 17 or other suitable methods andstructures. The substrate 2 may also be bonded to the heat sink 11, butpossibly at a different level than the high power IC's or PIC's 33 tokeep the active top layer of the high power IC's or PIC's 33 at the sameplanar level to benefit high frequency performance.

The second surface 5 of the substrate 2 may include a recess 20 or betiered, for receiving the components 3 at a bottom of the recess 20 oron a lower tier. Electrical contacts 18 may be provided on an upper tierof the second surface 5, e.g. on side walls surrounding the recess 20,for electrically connecting the components 3 and the high power ICs orPICs 33, via integrated or wire bonded leads, to mating electricalcontacts on a connecting device, e.g. a connecting PCB. The electricalconnector 18 may be comprised of suitable components for a ball gridarray (BGA), a land grid array (LGA) or a pin grid array (PGA). The sidewalls of the recess 20 may extend upwardly higher than the components 3and the high power ICs or PICs 33, thereby providing physical and RFprotection therefor.

A thermally conductive cover or lid 21 may be mounted over the secondsurface 5 of the substrate 2 to cover the recess 20 and the components3, along with all the wire-bonds 17, and to make contact withnon-sensitive portions of the components 3 and the high power ICs orPICs 33 mounted on the second surface 5 of the substrate 2 for thepurpose of providing a more direct path of heat dissipation for thecomponents 3 and the high power ICs or PICs 33 on the second side of thesubstrate 2 and on the exposed surface of the pedestal 15 or the heatspreader 16. One or more feet 23 extend from the lid 21 into contactwith the pedestal portion 15 or the heat spreader 16 for support/spacerfor the lid 21 and to provide a second thermally conductive path fromthe components 3 and the high power ICs or PICs 33 on both the first andsecond surfaces 4 and 5 of the substrate 2. The second thermallyconductive path may include the lid 21 making direct contact with themating PCB with a compliant thermal interface material, such as athermal epoxy, thermal pad or thermal grease. The contact from the lid21 to the mating PCB may then be achieved down to a thermallyconductive, e.g. copper, ground plane layer in the connecting PCB todissipate heat through the connecting PCB.

Potting or conformal coating inside the lid 21 may also be an option toimprove reliability and/or heat dissipation. A strain relief projection22 may be provided extending from the lid 21, integral therewith, to atleast partially surround the ends of the first and second optical fibers34 and 35, where they are coupled to the edge of the substrate 2. Thethermally conductive lid 21 may be comprised of a thermally andelectrically conductive material having a thermal conductivity of atleast 150 W/m° K, such as a metal, e.g. aluminum alloy 6061 (167 W/m° K)or copper (350 W/m° K).

Accordingly, the electro-optical and electronic components 3 may beattached to the top and bottom surfaces 4 and 5 of the substrate 2 andstill heat sink to both sides. This is achieved by incorporating each ofthe cavities 12 in the heat sink 11 to provide room for the components 3on the first surface 4, and the recess 20 in the substrate 2 to providea place for electronics on the bottom side 5. Components 3 on the firstsurface 4 may make direct contact with the heat sink 11, whilecomponents 3 on the bottom surface 5 may make thermal contact to theheat sink 11 and/or the bottom lid 21 to heat sink to the connectingPCB. Thus, every component 3 and high power IC or PIC 33 may be heatsunk in both thermally conductive path, e.g., opposite, directions andmore area is provided on the substrate 2 to place electrical components3 in a given volume.

The foregoing description of one or more embodiments of the inventionhas been presented for the purposes of illustration and description. Itis not intended to be exhaustive or to limit the invention to theprecise form disclosed. Many modifications and variations are possiblein light of the above teaching. It is intended that the scope of theinvention be limited not by this detailed description, but rather by theclaims appended hereto.

I claim:
 1. A semiconductor chip device comprising: a substrateincluding first and second sides, and an opening extending through thesubstrate between the first and second sides; first opto-electronic orelectronic components mounted on the first and second sides; a heat sinkmounted on the first surface in thermal contact with the components onthe first side, and including an extension extending through the openingwith an exposed surface parallel with the second side; and at least onesecond opto-electronic or electronic components mounted on the exposedsurface of the extension; wherein the heat sink provides a firstthermally-conductive path for the first components on the first side andeach of the second components on the exposed surface.
 2. The deviceaccording to claim 1, wherein the heat sink comprises a base with heatdissipating pins or fins extending outwardly therefrom, and theextension extending from the base through the opening; and wherein theheat sink comprises a single monolithic structure of thermallyconductive material.
 3. The device according to claim 1, wherein theheat sink comprises a base with heat dissipating pins or fins extendingoutwardly therefrom, and the extension extending from the base throughthe opening; and wherein the extension comprises a heat spreader sectioncomprised of a material with a coefficient of thermal expansion lowerthan that of the base.
 4. The device according to claim 3, wherein theheat spreader material has a coefficient of thermal expansion of lessthan 20×10⁻⁶ m/(m° K) @ 25° C., and a thermal conductivity greater than150 W/mK.
 5. The device according to claim 3, wherein the heat spreadermaterial has a coefficient of thermal expansion of less than 10×10⁻⁶m/(m° K) @ 25° C., and a thermal conductivity greater than 175 W/mK. 6.The device according to claim 1, wherein the heat sink includes a basein contact with the substrate; wherein the base includes cavitiestherein for receiving the first components on the first side of thesubstrate, thereby physically and RF shielding the first components onthe first side; and wherein the first components on the first side arein thermal contact with corresponding bottoms of the cavities.
 7. Thedevice according to claim 1, further comprising a thermally-conductivecover mounted over the second side of the substrate in thermal contactwith the first components on the second side and each of the secondcomponents on the exposed surface, providing a secondthermally-conductive path for the first components on the second sideand each of the second component on the exposed surface when a remoteheat sink is thermally coupled to the thermally-conductive cover.
 8. Thedevice according to claim 7, wherein the second thermally-conductivepath is in an opposite direction to the first thermally-conductive path.9. The device according to claim 7, wherein the thermally-conductivecover includes feet extending into contact with the heat sink, therebythermally coupling the first components on the first side to the secondthermally conductive path, and the first components on the second sideto the first thermally-conductive path.
 10. The device according toclaim 7, wherein the second side of the substrate includes a recesssurrounded by side walls for receiving the first and second components;and wherein the side walls extend higher than the first components inthe recess in the second side.
 11. A heat sink comprising: a baseadapted to be mounted on a first side of a substrate; thermallyconductive pins or fins extending from a first side of the base awayfrom the substrate providing a first thermally conductive path; cavitiesextending into a second side of the base and adapted to receiveopto-electronic or electronic components mounted on the first side ofthe substrate to physically and RF shield the opto-electronic orelectronic components; and an extension extending from the second sideof the base to extend through an opening in the substrate to a secondside of the substrate.
 12. The heat sink according to claim 11,comprising a single monolithic structure of thermally conductivematerial.
 13. The heat sink according to claim 11, wherein the extensioncomprises a heat spreader section comprised of a material with acoefficient of thermal expansion lower than that of the base.
 14. Theheat sink according to claim 13, wherein the heat spreader material hasa coefficient of thermal expansion of less than 20×10⁻⁶ m/(m° K) @ 25°C., and a thermal conductivity greater than 150 W/mK.
 15. The heat sinkaccording to claim 13, wherein the heat spreader material has acoefficient of thermal expansion of less than 10×10⁻⁶ m/(m° K) @ 25° C.,and a thermal conductivity greater than 175 W/mK.
 16. The heat sinkaccording to claim 11, further comprising a thermally-conductive coverto be mounted on the second side of the substrate in contact with theextension providing a second thermally conductive path.
 17. The deviceaccording to claim 16, wherein the second thermally-conductive path isin an opposite direction to the first thermally-conductive path.
 18. Thedevice according to claim 16, wherein the thermally-conductive coverincludes feet extending into contact with the extension, therebythermally coupling the opto-electronic or electronic components on thefirst side of the substrate to the second thermally conductive path, andopto-electronic or electronic components on the second side of thesubstrate or on the extension to the first thermally-conductive path.